Cell plasma membrane molecular transport

McCormick, J.I., Jette, M., Potier, M., Beliveau, R., Johnstone, R.M. (1991). Molecular size of a Na+-dependent amino arid transporter in Ehrlich ascites cell plasma membranes estimated by radiation inactivation. Biochemistry 30,3704-3709. 

These transporters represent established targets of many psychostimulants and antidepressants, which exert their potent psychotropic action via interference with transporter function, resulting in a rise in extracellular levels of monoamines (4,8). Some neuron-specific toxins can enter the cells through plasma membrane monoamine transporters, thereby revealing the additional functional role of transporters as a molecular gateway for neurotoxins (6,9). 

In neurons and non-neuronal cells, kinesin is associated with a variety of MBOs, ranging from synaptic vesicles to mitochondria to lysosomes. In addition to its role in fast axonal transport and related phenomena in non-neuronal cells, kinesin appears to be involved in constitutive cycling of membranes between the Golgi and endoplasmic reticulum. However, kinesin is not associated with all cellular membranes. For example, the nucleus, membranes of the Golgi complex and the plasma membrane all appear to lack kinesin. Kinesin interactions with membranes are thought to involve the light chains and carboxyl termini of heavy chains. However, neither this selectivity nor the molecular basis for binding of kinesin and other motors to membranes is well understood. 

Molecular communication is the characteristic information system in the bioinformation networks. The endocrine system, which is one of intermolecular information networks, may represent the feature of molecular communication. The gland is a collection of specialized cells that synthesize, store, and release hormones. A hormone, molecular information, is released into the extracellular fluid and transported via the blood to two types of cells target cells where the hormone acts, and other cells that degrade the hormone as schematically presented in Fig.l. In some systems the target cell and the degradation site are in the same organ or even the same cell. Both activities may even be located on the same plasma membrane. The receptor for the hormone is located on the surface of the plasma membrane. 

In recent years, tremendous progress has been achieved in the elucidation of the cellular and molecular mechanisms of insulin action. Tire acute cellular action of insulin is initiated by rapid clustering of occupied receptors on the cell surface. Within three minutes, a redistribution of glucose transporters from the cytoplasm to the plasma membrane can be measured lipolysis is also increased. 

Although the competition of two substrates for the same P-gp normally results in an inhibitory effect on the P-gp-mediated transport of the substrates, stimulation of P-gp-mediated efflux transport has been reported in some cases. The P-gp-mediated doxombicin efflux out of multidrug-resistant HCT-15 colon cells was significantly increased by some flavonoids (13). Similarly, rhodamine 123 and Hoechst 33342 stimulated the rate of P-gp-mediated transport of each other in P-gp-enriched plasma membrane vesicles isolated from Chinese hamster ovary CHRB30 cells (14). Interestingly, Hoechst 33342 transport was increased by daunorubicin and doxombicin, while rhodamine 123 transport was inhibited by daunombicin and doxombicin (14). These results strongly suggest that molecular mechanisms of P-gp interaction are quite complex and cannot be predicted readily. 

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